1. Field of the Invention
The invention relates to a power supply device, a power receiving device and a vehicle including the power receiving device, and a control method for a power supply system. Particularly, the invention relates to a power supply device and a power receiving device in a power supply system in which a power transmitting unit in the power supply device resonates with a power receiving unit in the power receiving device through an electromagnetic field to supply electric power from the power supply device to the power receiving device in a non-contact manner, a vehicle including the power receiving device, and a control method for the power supply system.
2. Description of Related Art
Japanese Patent Application Publication No. 2002-101578 (JP-A-2002-101578) describes a non-contact power transmitting device. The non-contact power transmitting device includes a primary coil, a secondary coil, first and second capacitors, a partial resonant inverter circuit, and a load. In the secondary coil, a voltage is induced by the primary coil. The first capacitor is connected in parallel or in series to the primary coil. The second capacitor is connected to the secondary coil. The partial resonant inverter circuit uses free oscillation due to the effect of resonance between the primary coil and the first capacitor. The load is provided at the output side of the secondary coil.
In the non-contact power transmitting device, the amplitude, frequency, and waveform of a voltage applied to the primary coil are changed in accordance with the inductance of the primary coil, which is changed in accordance with a change in a relative positional relation between the primary coil and the secondary coil. Thus, even when the relative positional relation between the primary coil and the secondary coil is changed, an output voltage or an output electric current is stabilized by changing the amplitude, frequency, and waveform of the voltage applied to the primary coil to increase the output.
Thus, in the non-contact power transmitting device, even when the relative positional relation between the primary coil and the secondary coil is changed, the output in the secondary side is easily stabilized (refer to the publication No. 2002-101578).
Three main technologies for transmitting electric power from a power supply device to a power receiving device in a non-contact manner are known. The three technologies include a technology in which electric power is transmitted through electromagnetic induction, a technology in which electric power is transmitted using microwaves, and a technology in which electric power is transmitted using a resonance method. Among them, the resonance method is a non-contact electric power transmission technology in which paired resonance units (for example, paired resonance coils) resonate with each other in an electromagnetic field (near field), and thus, electric power is transmitted through the electromagnetic field. The resonance method makes it possible to transmit great electric power, that is, several kW of electric power over a relatively long distance (for example, several meters).
When the voltage applied to the primary-side resonance unit (i.e., the power transmitting unit) is changed, the impedance of the power transmitting unit may match the impedance of a device other than the secondary-side resonance unit (i.e., the power receiving unit) or the impedance of space, and thus, electric power may be uselessly consumed.